Method for synchronizing an alternative audio stream

ABSTRACT

A method for synchronising a first audio stream, reproduced in the form of a sound signal by a reproduction device near a terminal, with an alternative audio stream received by the terminal. The terminal also receives a control stream representing the first audio stream reproduced on the reproduction device, the control stream and the alternative audio stream being synchronised according to a single time reference. the method includes: capturing a portion of the sound signal; transmitting to the reproduction device a command to suspend the reading of the first stream; obtaining a first data item representing at least one portion of the captured sound signal; detecting the first data item in the control stream and, when the first data item is detected in the control stream, transmitting to the reproduction device a command to resume reading the first stream; and reproducing the alternative audio stream received by the terminal.

TECHNICAL FIELD

The present invention relates to the audiovisual field and relates moreparticularly to the techniques for accessing an alternative soundtrackin the broadcasting of an audiovisual program.

PRIOR ART

The digital video and audio broadcasting techniques these days offer thepossibility for viewers to select different audio tracks when accessingan audiovisual program. For example, when accessing a VOD (Video OnDemand in English) content or a “Live” content, a user can choose alanguage from a set of languages available in order to view the programin the original version, in the French version or in any other versionoffered by the broadcaster of the content. Thus, when an alternativeaudio track is selected, it replaces the audio track offered by defaultby the broadcaster of the content.

It may be, for example, when a content is accessed at home that theselected audio track does not suit all the people present. For example,a film in original version may suit adults but not suit any children whoare watching the television at the same time. According to another caseof use, it may be that a viewer watching a sports competition wants tolisten to an alternative sporting commentary, not offered by thebroadcaster of the content. For example, when the competition isbroadcast live on television, a viewer can cut the sound on his or hertelevision and listen to the commentary on a radio station offeringanother, live, commentary for the same sporting event. In such a case,the radio-transmission delays of the televized and radio programs beingsubstantially different, the video contents played back on thetelevision set and the audio content played back on a radio set areoffset and do not make it possible to follow the program.

Similarly, this method also presents drawbacks when a viewer wants toaccess a greater variety of alternative audio contents by selecting, forexample, a radio commentary broadcast on the Internet.

In effect, for different technical reasons, the transmission delays ofsuch a content over the Internet network are greater than in the case ofa conventional transmission by radio channel or by a dedicatedcommunication network. Since the data packet routing delay is longer inthe Internet network, a loss of synchronization of the content from theInternet relative to that broadcast on the television is observed, evenwhen the contents are captured or produced synchronously. It is then notpossible to listen to a sporting commentary broadcast over the Internetinstead of the commentary offered on a television set, the commentariesthen generally being delayed by several seconds relative to the videoplayed back by the television set.

Techniques are known that make it possible to synchronize a contentdownloaded from the Internet with a televized program. For example, theEuropean patent application EP 20130173023 describes a method that makesit possible to trigger, on a terminal, the playback of a complementarycontent synchronously with the playback of a stream by a playback devicesuch as a television. Unfortunately, this method is not suitable fortriggering the reading, on a first terminal, of a first alternativeaudio stream broadcast continuously, such as a stream broadcastaccording to a streaming method, when this first stream is injected intothe network synchronously with a content intended to be played back on aplayback device such as a television, and this first stream undergoes adelay during the transmission in the Internet network.

There is therefore a clear need to synchronize the reading of a streamcurrently being broadcast over a first network to a first terminal withthe reading on a second terminal of a second stream currently beingbroadcast over a second network.

The invention improves this situation.

SUMMARY OF THE INVENTION

To this end, the invention relates to a method for synchronizing a firstaudio stream played back in the form of a sound signal by a playbackdevice in proximity to a terminal with an alternative audio streamreceived by the terminal, the method being noteworthy in that theterminal also receives a control stream representative of the firstaudio stream played back on the playback device, the control stream andthe alternative audio stream being synchronized according to a same timereference, and in that it comprises the following steps:

-   -   Capture of a part of the sound signal,    -   Emission, to the playback device, of a command to pause reading        of the first stream,    -   Obtaining of a first datum representative of at least a part of        the captured sound signal,    -   Detection of the first datum in the control stream, and    -   When the first datum is detected in the control stream:    -   Emission, to the playback device, of a command to resume reading        of the first stream, and    -   Playback of the alternative audio stream received by the        terminal.

Playback device should be understood to be a piece of equipment makingit possible to play back an audiovisual content. It may for example be atelevision, a digital decoder associated with a television or even a“set top box” type unit. The terminal used to receive an audio streamreplacing that played back on a television set or a decoder, receives atleast two mutually synchronized streams. At least one of the streams,called control stream, is representative of one of the audio tracks ofthe program currently being broadcast on the television. At least oneother of the streams received by the terminal is an audio trackalternative to that broadcast on the playback device. The terminal thusreceives the control stream with the same delay as the alternativestream. Since the control stream is comparable to the stream played backon the television, the terminal has a reference that makes it possibleto align the alternative content with the broadcast content. Theterminal captures, via a microphone of the terminal, a part of the soundsignal played back by the playback device and computes a datumrepresentative of the captured audio samples. The terminal then emits acommand to the playback device in order to pause the playback of theaudiovisual program. This pausing of the playback can for example bedone via a “pause” function offered by the playback device or by thebroadcasting network, during which the content currently being playedback on the playback device is memorized in a memory until the readingresumes. When the datum representative of the captured audio samples isdetected in the control stream, the streams are synchronized and theterminal emits a command to resume playback to the playback device andbegins playback of the alternative stream on the terminal.

Thus, the invention allows the synchronization of an alternative streamreceived by a terminal through a first network with a stream played backon a playback device via a second network, when the alternative streamis received with a delay in relation to the stream played back on aplayback device.

According to a particular embodiment, the method is such that the firstrepresentative datum is an acoustic imprint computed from at least apart of the captured sound signal.

An acoustic imprint makes it possible to uniquely identify a soundextract. The use of an acoustic imprint makes it possible to identify asound extract from a playback device and locate this extract withinanother stream in order to estimate and compensate the offset betweenthe two streams.

According to a particular embodiment, the method is such that it alsocomprises the following steps:

-   -   Obtaining, from the control stream, of a second datum        representative of a part of the audio signal of which the        control stream is representative, and memorizing of a first time        stamp,    -   Capture of the sound signal played back by the playback device,    -   Detection of the second datum from the captured sound signal,        and    -   When the second datum is detected in the captured signal:    -   Determination of a second time stamp, and    -   Application of a delay to the alternative audio stream, the        delay corresponding to the time interval between the first and        second stamps.

The commands to pause and resume reading do not always offer theaccuracy necessary for the perfect synchronization of the streamsreceived on the terminal with those played back by the playback device.In order to mitigate this drawback, the method according to theinvention proposes obtaining a datum representative of a part of thestream received by the terminal and searching for this imprint in thesound signal captured via a microphone of the terminal, in order tocompute a possible delay of the playback device in relation to thestreams received by the terminal. This delay is then applied to thestreams played back by the terminal in order to improve thesynchronization when the streams received by the terminal are in advancerelative to the content played back by the playback device.

According to a particular embodiment, the method is such that the secondrepresentative data is an acoustic imprint computed from a part of anaudio signal.

An acoustic imprint makes it possible to uniquely identify a soundextract. The use of an acoustic imprint makes it possible to identify asound extract and locate it within another stream in order to estimateand compensate the offset between the two streams.

According to a particular embodiment, the method is noteworthy in thatthe control stream is an audio stream.

The control stream can be an audio stream corresponding to the contentcurrently being played back on a playback device such as a television.Thus, the control stream can be a duplication of the soundtrack of anaudiovisual content currently being played back. This control stream canthen serve as a basis for the computation of an acoustic imprint which,when it corresponds to an acoustic imprint computed from the soundsignal generated by the television, makes it possible to estimate andcompensate the offset observed between the streams.

The control stream can also be a data stream comprising a succession ofacoustic imprints precomputed from the soundtrack of the contentcurrently being played back on the playback device. Such an arrangementavoids requiring the terminal to compute the imprint on the receivedcontrol stream and lightens the processing operations required for thesynchronization of the streams.

According to a particular embodiment, the method is such that aplurality of control streams are received by the terminal, the controlstreams corresponding to the audio tracks available on the playbackdevice.

Conventionally, some playback devices offer the possibility to the usersof selecting a particular audio track from a plurality of availableaudio tracks. For example, it is common practice for a digital decoderto allow a user to select a language from a set of available languages.The method provides for all the audio tracks made available to the userby the playback device to be also transmitted to the terminal in theform of a plurality of mutually synchronized control streams and with atleast one alternative audio stream, the control stream from which datarepresentative of sound extracts are obtained. The method thus allowsthe synchronization of an alternative stream received on the terminalwith the content played back on the playback device, whatever the audiotrack selected on the playback device.

According to another aspect, the invention relates to a method foraligning a first audio stream played back by a playback device inproximity to a terminal with an alternative audio stream received by theterminal, the method being such that the terminal also receives acontrol stream representative of the stream played back on the playbackdevice, the alternative audio stream and the control stream beingsynchronized according to a same time reference, and such that itcomprises, on receipt of a message comprising an indication according towhich the playback of the stream has been paused following the executionby a second terminal of the synchronization method, the following steps:

-   -   Obtaining, from the control stream, of a second datum        representative of a part of the audio signal of which the        control stream is representative, and memorizing of a first time        stamp,    -   Capture of the sound signal played back by the playback device,    -   Detection of the second datum in the captured sound signal, and

When the second datum is detected from the captured signal:

-   -   Determination of a second time stamp, and    -   Application of a delay to the alternative audio stream, the        delay corresponding to the time interval between the first and        second stamps, and    -   Playback of the alternative audio stream received by the        terminal.

When the playback is paused on the playback device, a message is sent tothe terminals. This message comprises an indication according to whichthe playback of the first stream by the playback device has been pausedfollowing the prior execution of the synchronization method by anotherterminal. Such an arrangement advantageously allows a second terminalwanting to synchronize the reading of an alternative stream with thereading of a stream on the playback device, to dispense with the stepsof capture of a part of the sound signal played back by the playbackdevice, of emission of a command to pause the reading of the firststream, of detection of the first imprint and of emission of a commandto resume the reading of the first stream.

According to another aspect, the invention relates to a device forsynchronizing a first audio stream played back by a playback device inproximity with an alternative audio stream received by the device, thedevice being such that it also receives a control stream correspondingto the first audio stream played back on the playback device, thecontrol stream and the alternative audio stream being synchronizedaccording to a same time reference, and in that it comprises:

-   -   An audio interface, adapted to capture a part of the sound        signal played back by the playback device,    -   A communication interface, adapted to receive at least an        alternative audio stream and a control stream and to emit, to        the playback device, a command to pause the reading of the first        stream,    -   A signal processing unit, adapted to obtain a first datum        representative of at least a part of the captured sound signal,    -   A detector, configured to detect, in the control stream, the        first computed imprint,

The communication interface being also adapted to emit, when the firstimprint is detected in the control stream, a command to resume thereading of the first stream to the playback device, and the audiointerface being also adapted to play back the alternative audio streamreceived by the device.

The invention relates also to a terminal comprising a synchronizationdevice as described previously.

The devices and terminals offer advantages similar to those of themethod presented previously.

In a particular embodiment, the different steps of the method accordingto the invention are determined by instructions of computer programs.

Consequently, the invention also targets a computer program comprisinginstructions suitable for implementing steps of a method as describedabove, when the program is run by a processor.

This program can use any programming language, and be in the form ofsource code, object code, or intermediate code between source code andobject code, such as in a partially-compiled form, or in any otherdesirable form.

The invention also targets a computer-readable storage medium on whichis stored a computer program comprising instructions for the executionof the steps of the method.

The information medium can be any entity or device capable of storingthe program. For example, the medium can comprise a storage means, suchas a ROM, for example a CD ROM or a microelectronic circuit ROM, a flashmemory, or even a magnetic storage means, for example a diskette (floppydisk) or a hard disk.

Also, the information medium can be a transmissible medium such as anelectrical or optical signal, which can be routed via an electrical oroptical cable, by radio or by other means. The program according to theinvention can in particular be downloaded over a network of Internettype.

Alternatively, the information medium can be an integrated circuit inwhich the program is incorporated, the circuit being adapted to executeor to be used in the execution of the method concerned.

The various embodiments or features mentioned above can be addedindependently or in combination with one another, to the steps of thesynchronization method.

LIST OF FIGURES

Other features and advantages will emerge from reading preferredembodiments described with reference to the figures in which:

FIG. 1 illustrates an architecture suitable for implementing theinvention according to a particular embodiment,

FIG. 2 illustrates the main steps of the synchronization methodaccording to a particular embodiment of the invention,

FIG. 3 illustrates the main steps of the synchronization methodaccording to another particular embodiment of the invention,

FIG. 4 illustrates the main steps of the alignment method according to aparticular embodiment of the invention, and

FIG. 5 illustrates the architecture of a device suitable forimplementing the invention according to a particular embodiment.

DETAILED DESCRIPTION

FIG. 1 illustrates an architecture suitable for implementing theinvention according to a particular embodiment. The architecturecomprises a television 101 to which is connected a digital decoder 102.The television and the decoder constitute what will hereinafter in thisdescription be called a playback device. Such a playback device isadapted to receive, decode and play back an audiovisual signal receivedvia a communication network or by microwave or satellite broadcast. Itis for example a television set connected to a terrestrial digital TVreceiver or even a decoder of set top box type connected to atelecommunication network via a high bit rate network. The playbackdevice thus allows a user to view contents broadcast by a contentprovider. The digital decoder 102 and the television set 101 can also beincorporated in one and the same item of equipment, such as a connectedtelevision or a personal computer. The decoder 102 comprises afunctionality allowing the user to momentarily pause the playback of acontent. The audiovisual content received is then memorized in a memoryof the decoder so that a user can order the resumption of the playbackwithout losing the content broadcast during the pause period. The usercan then continue viewing with a delay. Such a functionality of pausingand resuming the reading with a delay is known and is generallyaccessible via a remote control associated with the decoder. Somedecoders also offer access to this function through API (ApplicationProgramming Interfaces) which make it possible, for example, to controlthe decoder from applications developed on independent terminals, suchas, for example, from a smartphone or a tablet.

In this example, the content played back on the playback device isbroadcast by a broadcast server 104 through a multicast contentdistribution network 105.

The architecture of FIG. 1 also comprises a mobile terminal 106. It is,for example, a terminal of smartphone, tablet or personal assistant typeor even a computer comprising a processing unit comprising a processorlinked to one or more RAM (Random Access Memory) memories. The processoris configured to execute instructions loaded into the memory. Inparticular, the processor is adapted to execute instructions fordecoding an audio content. The terminal also comprises a networkinterface adapted to exchange data with other terminals or servers via awireless link of 3G, Wifi or Bluetooth type for example. With thiscommunication interface, the terminal can in particular emit, through alocal area network 100, commands to control the decoder 102 and receive,via the communication network 108, contents made available by a server107. The terminal also comprises an audio interface adapted to convertdigital signals into analog signals and vice versa. In particular, theterminal can capture and store, in the form of digital data, a soundsignal from a microphone incorporated into the terminal and generate,from a digital audio content, a sound signal via a loudspeaker orindividual earphones. The terminal 106 is thus adapted to download audiostreams from the server 107, decode them and play them back continuouslythrough a loudspeaker or a headset. The terminal 106 is also positionedin proximity to the playback device so as to be able to capture a soundsignal generated by a loudspeaker 103 of the playback device.

The main steps of the synchronization method will now be described withreference to FIG. 2, according to a first embodiment of the invention.

In a first step 200, the terminal receives at least one alternativestream and at least one control stream synchronized according to a sametime reference. The streams are for example received following a requestsent by the terminal 106 to the server 107. For that, the terminal candownload a file describing the streams available on the server 107, suchas, for example, a so-called “manifest” file describing the availableaudio streams and the means for accessing them. After reading this file,the terminal simultaneously subscribes to all the audio streams, decodesthem and offers the user the choice between all the versions availablein the manifest. The streams are transmitted to the terminal via acontinuous downloading protocol, such as, for example, according to theMicrosoft' “Smooth Streaming” protocol. Other streaming protocols can ofcourse be used for the implementation of the invention, such as, forexample, RTP/RTSP (Real Time Protocol/Real Time Streaming Protocol) orHLS (http Live Streaming). The audio stream received corresponds to anaudio track selected by the user of the terminal 106 to replace thesoundtrack of an audiovisual content currently being played back on theplayback device. It concerns for example a dubbing in a language whichis not available or which has not been selected on the playback device.The control stream is representative of an audio stream currently beingplayed back on the playback device.

According to a particular embodiment of the invention, the controlstream is an audio stream of a quality identical to the audio streamplayed back on the playback device. It can also be a copy of lesserquality of the audio stream played back on the playback device, encodedfor example according to a different bit rate and/or format.

According to another particular embodiment, the control stream comprisesdata computed from the audio stream currently being played back on theplayback device. It is for example a succession of imprints orsignatures computed from at least one audio stream available forplayback on the playback device.

The at least one audio stream and at least one control stream aresynchronized according to a same time reference and broadcastsimultaneously.

In the step 201, the terminal captures a part of the sound signalcorresponding to the first audio stream played back by the playbackdevice. The capture of the sound signal is performed using the audiointerface and the microphone of the terminal. This step makes itpossible to obtain a digital representation of a part of the soundsignal generated by the playback device of a predefined duration, forexample of a duration of a few seconds.

The terminal emits, in the step 202, a command to pause the playback ofthe content to the playback device when a part of the signal iscaptured. This command is emitted by using a communication interface ofthe terminal. For example, the command can be inserted into an httprequest emitted through a wireless connection of Wifi type andpropagated to the playback device via a local area network to which theplayback device is connected. The playback device can comprise a webserver suitable for receiving such a request and interpreting commandsincluded therein, and in particular a pause command inserted for exampleinto a header or the body of the http request. According to anotherexample, the command can be transmitted via an ad hoc Bluetoothconnection. On receipt of such a command, the playback device pauses theplayback and continues to receive the stream currently being playedback. The data of the stream received are then memorized in a memory ofthe device so that the playback can subsequently resume and the contentcan be viewed in full. The web server of the playback device can then,according to a particular embodiment, emit a response to the terminalhaving emitted the request. The response received by the terminal cancomprise an indication according to which the command to correctly beenexecuted, or, if appropriate, an indication according to which thecommand has not been able to be executed.

The terminal then obtains, in a step 203, a first datum representativeof at least a part of the sound signal captured in the step 201.According to a particular embodiment, such a representative datum is anacoustic imprint generated from the captured audio signal. Differentmethods for computing an imprint can be used to implement the invention.For example, the international patent application WO 2013095893 A1describes a method for computing an acoustic imprint suitable foridentifying a content broadcast continuously on a television. Accordingto another example, the imprint can also be computed according to themethod described in the European patent application EP 2677764 A1. Suchan imprint computation algorithm can be implemented by a sequence ofinstructions executed by a processing unit of the terminal.

According to a particular embodiment, the first representative datum isa datum added to the audio signal and adapted to be retained upon thepropagation of the sound signal, without being detectable to the humanear. The datum is then obtained by a signal processing operation appliedto the samples received, making it possible to find the datum added tothe signal. The patent U.S. Pat. No. 5,940,135 A describes such atechnique. The representative datum can then be a synchronizationinformation item associated with an extract of the audio signal, suchas, for example, a time stamp or a unique identifier of the extract.

In the step 204, the terminal detects, in the control stream, therepresentative datum obtained. According to a particular embodiment, thecontrol stream is an audio stream corresponding to the stream currentlybeing played back on the playback device. The detection step thenconsists in searching in the control stream for the representative datumobtained in the step 203. For that, the terminal implements, from audiodata decoded from the control stream, the same algorithm as that used inthe step 203 in order to obtain a second datum representative of thestream. The datum is detected when the second representative datumcorresponds to the datum obtained in the step 203. The step ofcomputation and of comparison of the representative data is repeated forthe new data received until the actual detection of the datum.

According to a particular embodiment, the control stream consists of asuccession of data representative of the stream played back on theplayback device. It can be, for example, a succession of precomputedimprints corresponding to different parts of the stream currently beingplayed back on the playback device. Thus, the terminal does not have tocompute the imprint, a simple comparison of the datum obtained in thestep 203 with the data transmitted in the control stream is sufficientfor the detection. The control stream can also consist of a series ofsynchronization information items corresponding to different soundextracts from the stream played back on the playback device. Thesesynchronization information items can then be compared with thoseobtained in the step 203 from the sound signal captured to perform thedetection.

When the first datum obtained in the step 203 is detected in the controlstream in the step 204 the terminal emits, to the playback device, acommand to resume the reading of the first stream in a step 205. Theplayback of the content on the playback device was paused on obtainingthe first representative datum in the step 203. The detection of thisfirst datum in the control stream indicates that the control stream issynchronized with the stream currently being played back on the playbackdevice. Since the control stream is received by the terminalsynchronously with at least one other alternative audio stream, thedetection also indicates that the latter is also synchronized with thestream currently being played back on the playback device. The terminalthen emits a command to resume the reading to the playback device andbegins, in the step 206, the decoding and the playback, via aloudspeaker or a headset of the terminal for example, of the alternativeaudio stream received.

The method thus makes it possible to synchronize an alternative audiostream received on the terminal with an audiovisual content played backon a playback device, when the alternative stream is delayed relative tothe audiovisual content.

It may be that the playback pause and resume functionality on theplayback device does not offer sufficient accuracy to obtain asatisfactory synchronization. In this case, the latency relating to theprocessing of the command to resume reading can cause a delay in theplayback of the content by the playback device relative to the streamsreceived by the terminal.

The invention provides a solution to this drawback, according to aparticular embodiment which will now be described with reference to FIG.3.

The step 300 referenced in FIG. 3 comprises steps similar to the steps200 to 206 described previously with reference to FIG. 2. In this step300, the playback is momentarily paused on the playback device until thecontrol stream received by the terminal is synchronized with the streamplayed back on the playback device. For that, the terminal computes, forexample, an imprint from an extract of the sound signal emitted by theplayback device and pauses the playback until this imprint is detectedin the control stream received by the terminal.

In the step 301, the terminal obtains, from the control stream, a seconddatum representative of a part of an audio signal, and memorizes a firsttime stamp, the first time stamp corresponding for example to theinstant of presentation of the last audio sample of the part of theaudio signal that was used to obtain the second representative datum.The representative datum obtained corresponds for example to an acousticimprint computed from a decoded extract from the control stream, whenthe control stream is an audio stream.

Such an imprint can for example be computed according to the techniquedescribed in the international patent application WO 2013095893 A1 oreven according to the method described in the European patentapplication EP 267764 A1. When, according to a particular embodiment,the control stream is not an audio stream but consists, for example, ofa succession of precomputed imprints or of synchronization informationitems, the obtaining of the second representative datum consists inreading the datum in the control stream.

The terminal, in the step 302, performs a capture of the sound signalgenerated by the playback device. For that, the terminal implements anaudio acquisition interface comprising a microphone and a signalsampling module.

The terminal then detects, in the step 303, the representative datum inthe captured signal. For that, according to a particular embodiment, theterminal can compute an imprint according to the same method as in thesteps 302 and perform a comparison with the imprint obtained in the step301. The steps of capture, of obtaining of a second representative datumand of comparison of this datum with that obtained in the step 301 arerepeated from new samples captured as long as the datum obtained in thestep 301 is not detected in the captured sound signal. When the secondrepresentative datum is detected, a time stamp corresponding, forexample, to the instant of capture of the last sample used to obtain thesecond representative datum is memorized in the step 304. As a variant,the first and second time stamps can respectively correspond to theinstants of reception and of capture of the first sample used to obtainthe corresponding representative datum, the important thing being thatthe first and second stamps correspond substantially to the same soundextract in the captured signal and the control stream. The first andsecond stamps are obtained from a same clock of the terminal. Thus, thedifference between the second and the first stamps corresponds to theoffset observed between the playback of the audiovisual content by theplayback device and the receipt of the control stream by the terminal.

In the step 305, the playback of the alternative audio stream receivedby the terminal is delayed by the offset value measured between the twostamps. For that, the data decoded from the second stream are memorizedin a buffer memory of the terminal. According to a particularembodiment, the playback of the decoded samples is paused for a durationcorresponding to the measured delay, the decoded samples being memorizedin the buffer memory during the pause period. It is thus possible tocompensate the delay to synchronize the content played back on theplayback device with the alternate audio stream received by theterminal, with an accuracy which depends on the measurement of thedelay. For example, when the delay is estimated by comparison of theimprints, the streams can be synchronized with an accuracy of the orderof a few tens of milliseconds.

According to a particular embodiment, a plurality of control streams arereceived by the terminal, the control streams corresponding to the audiotracks available on the playback device. So as to be able to match arepresentative datum, such as an acoustic imprint characteristic of apart of the content currently being played back on the playback device,with a datum representative of a part of a control stream received onthe terminal, the content played back on the playback device and thatreceived by the terminal must correspond. Now, when several audiotracks, corresponding for example to several languages, are availablefor the content currently being played back on the playback device, theterminal has no a priori knowledge of the audio track selected by theuser. Thus, the method according to the invention proposes that aplurality of control streams be received by the terminal, each controlstream corresponding to an audio track available on the playback device.Thus, in the step 204, the first representative datum is detected ineach of the control streams received by the terminal. The detectiontakes effect when the representative datum is detected in one of thecontrol streams. Similarly, in the step 301, a second representativedatum such as an acoustic imprint is obtained for each control streamreceived, these different data being compared in the step 303 with adatum obtained from the captured sound signal. Thus, it is possible tosynchronize the content played back on the playback device with analternative audio stream received by the terminal, whatever the languageselected by the user on the playback device.

It may be that a second terminal tries to synchronize an alternativeaudio stream with a content currently being played back on a playbackdevice while the synchronization method is already currently beingexecuted on a first terminal. In this case, the second terminal canbenefit, without executing them, from the steps 201 to 205 alreadyperformed or currently being performed by the first terminal. This otheraspect of the invention relates to an alignment method which will now bedescribed with reference to FIG. 4, according to a particularembodiment.

In a first step similar to the step 200 described with reference to FIG.1, the terminal receives at least one alternative audio stream and atleast one control stream representative of a stream currently beingplayed back on a device, the received streams being synchronized withone another according to a same time reference.

In the step 400, the terminal receives a message comprising anindication according to which the playback of a content on the playbackdevice is paused following the execution by a second terminal of thesynchronization method. This message can be received following theemission of a command to pause the playback to the playback device, orelse following the emission of a command to consult the status of theplayback device. This message can also be broadcast by another terminalwhich executes the synchronization method. The receipt of this messageinforms the terminal that a certain number of steps, and in particularthe steps 202 of pausing of the playback and 205 of resumption of theplayback must not be performed because they would risk desynchronizingthe first terminal. Thus, the playback of the content on the playbackdevice does not have to be delayed.

The terminal then executes the steps 301 to 305 in accordance with thosedescribed previously with reference to FIG. 3, in order to align thealternative stream received with the content played back by the playbackdevice.

When the alternative stream is aligned with the content currently beingplayed back, the terminal can trigger the playback of the alternativestream in accordance with the step 206 described with reference to FIG.1.

FIG. 5 illustrates, according to a particular embodiment of theinvention, a device 500 implementing the synchronization method.

The device comprises a storage space 501, for example a memory MEM, aprocessing unit 502 equipped for example with a processor PROC. Theprocessing unit can be driven by a program 503, for example a computerprogram PGR, implementing the synchronization method as described in theinvention with reference to FIG. 2, and in particular the steps ofreceipt of an alternative audio stream synchronized with a controlstream, of capture of a part of the sound signal played back by theplayback device, of emission, to the playback device, of a command topause the reading of the first stream, of obtaining of a first datumrepresentative of at least a part of the captured sound signal, ofdetection of the first datum in the control stream, and, when the firstdatum is detected in the control stream, of emission, to the playbackdevice, of a command to resume the reading of the first stream, and ofplayback of the alternative audio stream received by the terminal.

On initialization, the instructions of the computer program 503 are forexample loaded into a RAM (Random Access Memory in English) memorybefore being executed by the processor of the processing unit 502. Theprocessor of the processing unit 502 implements the steps of thesynchronization method according to the instructions of the computerprogram 503.

For that, the device comprises, in addition to the memory 501,communication means 505, such as, for example, a wireless networkinterface COM, allowing the device to connect to a telecommunicationnetwork and exchange data with other devices via the telecommunicationnetwork, and in particular emit commands to pause and resume reading toa playback device and receive one or more streams currently beingbroadcast by a server. The device also comprises an audio interface 504adapted to convert digital signals into analog signals and vice versa.In particular, the device can capture and store in the memory 501, inthe form of digital data, a sound signal from a microphone 506 andgenerate, from a decoded digital audio content, a sound signal via aloudspeaker 507 or individual earphones. The device also comprises aprocessing unit 509 adapted to decode a compressed audio stream. Thedevice is thus adapted to receive audio streams from the server, decodethem and play them back continuously through a loudspeaker or a headset.

The device 500 also comprises a signal processing unit 510 adapted toobtain a datum representative of a part of an audio signal. For example,the unit 510 comprises a processor configured to execute instructions tocompute an acoustic imprint representative of an extract of an audiosignal captured by the microphone 506 and sampled by the audio interface504, or else instructions to extract data added in a digital soundsignal.

The device finally comprises a detector 508, configured to detect, in acontrol stream, an acoustic imprint computed by the processing unit 510.The detector can be implemented by a processor configured to executeinstructions suitable for performing a comparison of two digitalimprints.

The invention can be implemented on terminals of smartphone type, ontablets or personal computers and makes it possible to enrich thetraditional television experience such as streaming, video on demand(VOD) or catch-up television.

1. A method for synchronizing a first audio stream played back in theform of a sound signal by a playback device in proximity to a terminalwith an alternative audio stream received by the terminal, the methodcomprising capturing, by the terminal, a part of the sound signal, theterminal also receiving a control stream representative of the firstaudio stream played back on the playback device, the control stream andthe alternative audio stream being synchronized according to a same timereference, emitting, to the playback device, command to pause reading ofthe first stream, obtaining a first datum representative of at least apart of the captured sound signal, detecting the first datum in thecontrol stream, and when the first datum is detected in the controlstream: emitting, to the playback device, a command to resume reading ofthe first stream, and playing back the alternative audio stream receivedby the terminal.
 2. The method as claimed in claim 1, wherein the firstrepresentative datum is an acoustic imprint computed from at least apart of the captured sound signal.
 3. The method as claimed in claim 1,further comprising: Obtaining, from the control stream, a second datumrepresentative of a part of the audio signal of which the control streamis representative, and memorizing a first time stamp, capturing thesound signal played back by the playback device, detecting the seconddatum in the captured sound signal, and when the second datum isdetected in the captured signal: determining a second time stamp, andapplying a delay to the alternative audio stream, the delaycorresponding to the time interval between the first and second stamps.4. The method as claimed in claim 1, wherein the second representativedatum is an acoustic imprint computed from a part of an audio signal. 5.The method as claimed in claim 1, wherein the control stream is an audiostream.
 6. The method as claimed in claim 1, wherein a plurality ofcontrol streams are received by the terminal, the control streamscorresponding to the audio tracks available on the playback device.
 7. Amethod for aligning a first audio stream played back in the form of asound signal by a playback device in proximity to a terminal with analternative audio stream received by the terminal, the methodcomprising: the terminal receiving the alternative audio stream andreceiving a control stream representative of the first audio streamplayed back on the playback device, the control stream and thealternative audio stream being synchronized according to a same timereference, and on receipt of a message comprising an indicationaccording to which playback of the first audio stream by the playbackdevice has been paused performing the following acts: obtaining, fromthe control stream, datum representative of a part of the audio signalof which the control stream is representative, and memorizing a firsttime stamp, capturing the sound signal played back by the playbackdevice, detecting the second datum in the captured sound signal, andwhen the datum is detected from the captured signal: determining asecond time stamp, and applying a delay to the alternative audio stream,the delay corresponding to the time interval between the first andsecond stamps, and playing back the alternative audio stream received bythe terminal.
 8. A device for synchronizing a first audio stream playedback by a playback device in proximity with an alternative audio streamreceived by the device, wherein the device receives a control streamcorresponding to the first audio stream played back on the playbackdevice, the control stream and the alternative audio stream beingsynchronized according to a same time reference, and wherein the devicecomprises: an audio interface, adapted to capture a part of the soundsignal played back by the playback device, a communication interface,adapted to receive at least an alternative audio stream and a controlstream and to emit, to the playback device, a command to pause readingof the first stream, a signal processing unit, adapted to obtain a firstdatum representative of at least a part of the captured sound signal, adetector, configured to detect, in the control stream, the firstcomputed imprint, wherein the communication interface is also adapted toemit, when the first imprint is detected in the control stream, acommand to resume the reading of the first stream to the playbackdevice, and the audio interface is also adapted to play back thealternative audio stream received by the device.
 9. A terminal,comprising the device as claimed in claim
 8. 10. (canceled)
 11. Anon-transitory processor-readable information medium, on which is storeda computer program comprising instructions for executing asynchronization method when the program is run by a processor ofterminal, wherein the synchronization method comprises synchronizing afirst audio stream played back in the form of a sound signal by aplayback device in proximity to the terminal with an alternative audiostream received by the terminal, including: capturing, by the terminal,a part of the sound signal, the terminal also receiving a control streamrepresentative of the first audio stream played back on the playbackdevice, the control stream and the alternative audio stream beingsynchronized according to a same time reference, emitting, to theplayback device, a command to pause reading of the first stream,obtaining a first datum representative of at least a part of thecaptured sound signal, detecting the first datum in the control stream,and when the first datum is detected in the control stream: emitting, tothe playback device, a command to resume reading of the first stream,and playing back the alternative audio stream received by the terminal.